Freepbx14 ucp webrtc phone not working

Hi all.

I had a thread open a while ago (Freepbx14 UCP reachable but unable to dial out) and tried yesterday again. But still the same issue. WebRTC Phone is registered (green), asterisk shows the 999xxx extension as ok, but no phone status in UCP. I suppose people have it running? If so, any special configurations? I use Firefox 54. What version are supposed to work?

thanks and cheers